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50 CHEMISTRY FOR THE UTTERLY CONFUSED
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4-1 Molarity (M)
Quick Tip
Our goal in this chapter is to help you learn about reactions in aqueous solutions,
including titrations. We will present a set of solubility rules you can use to
predict whether or not precipitation will take place when two solutions are
mixed. You may want to talk to your instructor and/or check your text for other
solubility rules. These rules will be useful as you learn to write net ionic equations.
If you are unsure about mass/mole relationships, you may want to review
Chapter 3. And remember—Practice, Practice, Practice.
A solution is a homogeneous (the same throughout) mixture composed of a
solvent, the part of the solution that is present in the greater amount, and one
or more solutes, the substance(s) present in the smaller amount. A solution in
which water is the solvent is an aqueous solution. Aqueous solutions are the primary
focus of this chapter. We will investigate other solutions in Chapter 12.
One of the most important properties of a solution is its concentration—the relative
amount of solute in the solution. One of the most common ways of
expressing concentration is molarity. Molarity (M) is the moles of solute per
liter of solution. (We will see other ways of expressing the concentration of a
solution later.) For example, suppose you dissolved 0.500 mol of sucrose, cane
sugar, in enough water to make 1.00 L of solution. The molarity of that sucrose
solution would be:
0.500 mol sucrose/1.00 L solution 0.500 mol/L 0.500 M
In preparing a specific molar solution, you should dissolve the required amount
of solute in a little solvent and then dilute to the required volume.